On the recent mobile phone market, types of mobile phones having built-in camera modules have been dominant. These camera modules are meant to be embedded in the mobile phones. Therefore, they face greater demands for being compact and lightweight, compared with camera modules to be embedded in digital cameras.
Among such camera modules, there have been an increasing number of camera modules that (i) operate their autofocus (AF) systems with the use of lens drive devices and (ii) are mounted on electronic devices such as mobile phones. Examples of lens drive devices that have been developed so far encompass those employing stepper motors, piezoelectric elements, and VCM (Voice Coil Motor). Such lens drive devices have already been distributed on the market.
Meanwhile, now that such camera modules having autofocus (AF) systems have become new standards, a system for image stabilization is becoming the focus of attention as a next distinctive feature. Although a system for image stabilization has been widely used for digital cameras and camcorders, there have been only a few mobile phones equipped with systems for image stabilization, due to the issue of a limited size of mobile phone. Nevertheless, it is expected that mobile-phone-specified camera modules having systems for image stabilization will be more widespread in years to come, and, in fact, a new system (configuration) for image stabilization, which can be made compact, has been suggested.
A camera module capable of image stabilization and intended to be incorporated into a mobile phone is disclosed in Patent Literature 1, for example. The technique disclosed in Patent Literature 1 relates to an Optical Image Stabilizer (OIS).
The optical image stabilizer disclosed in Patent Literature 1 has a structure in which a conventional AF camera module called an imaging unit (movable module) is supported by four suspension wires at four corners of the imaging unit, and the imaging unit is driven in directions of two axes each orthogonal to an optical axis, thereby stabilizing an image. A mechanism for driving the imaging unit is such that magnets are provided on four circumferential side surfaces of a cover section on which the imaging unit is mounted, and coils are provided at yokes of a fixed part so as to face the magnets. This mechanism enables the imaging unit (movable module) to stabilize an image independently in the two axes orthogonal to the optical axis. According to Patent Literature 1, the optical image stabilizer disclosed therein is designed such that the imaging unit as a whole is driven in directions orthogonal to the optical axis. A generally employed arrangement for image stabilization is such that relative displacement is provided between an image pickup lens and an image pickup element.
In a case of an AF camera module involving fixing of the lenses to the lens driving device, it is necessary to appropriately set an initial position of the lenses in an optical axis direction with respect to an image pickup element. Otherwise, a defocused image is caused.
In view of this, among the conventional AF camera modules, dominating AF camera modules have a mechanism in which a screw structure is provided in a lens barrel (housing in which a plurality of lenses are built) and a lens holder so that the position of the lenses in an optical axis direction is adjusted.
On the other hand, in a case of a fixed-focus camera module which does not require movement of lenses in carrying out the setting for an initial position of the lenses, it is possible to set the initial position of the lens with high precision by directly attaching the lens or a lens holder holding the lenses to an image pickup element or a member holding the image pickup element.
For example, Patent Literature 2 discloses an AF camera module which does not have a screw structure and in which focus adjustment for the setting of an initial position during the production of the AF camera module is not performed with a screw.
FIG. 23 shows a cross sectional view of a representative example of the AF camera module disclosed in Patent Literature 2.
As shown in FIG. 23, an AF camera module 100 disclosed in Patent Literature 2 includes an optical section 101 serving as an image pickup optical system, a lens driving device 102 which drives the optical section 101, and an image pickup section 103 which carries out photoelectric conversion of light having passed through the optical section 101. The image pickup section 103 includes a sensor section 104 and a substrate 105 on which the sensor section 104 is mounted. The sensor section 104 includes a glass substrate 120, a sensor chip 121, and a sensor cover 122.
The optical section 101 includes a plurality of image pickup lenses 106 and a lens barrel 107 which holds the image pickup lenses 106. The lens barrel 107 is fixed to a lens holder 108 in the lens driving device 102. The lens holder 108 is supported by two (upper and lower) springs 109a and 109b so as to be movable in an optical axis direction with respect to a fixed section. Coils 110 are fixed on the periphery of the lens holder 108. The fixed section includes a yoke 111, a permanent magnet 112, a cover 114, a base 115 etc. The lens driving device 102 is mounted on a sensor cover 122.
The lens barrel 107 and the lens holder 108 are not threaded. Accordingly, the lens barrel 107 is so positioned as to abut the upper surface of the sensor cover 122 while the lens holder 108 is located at a mechanical end on an infinite-distance side, and the lens barrel 107 is adhesively fixed to the lens holder 108 with an adhesive 124.
This configuration enables the height of the image pickup lenses 106 with respect to the sensor chip 121 to have only minor tolerances, such as a tolerance for the thickness of the sensor cover 122 and a tolerance for the position where the image pickup lenses 106 are attached in the lens barrel 107. Consequently, it is possible to determine the initial position of the image pickup lenses 106 with high precision without adjusting the height of the lenses with use of a screw, and so it is possible to omit a focus adjustment process for determining the initial position.